• Wind and Structures
• /
• v.7 no.2
• /
• pp.89-106
• /
• 2004

The response of tall buildings to gust buffeting is usually evaluated assuming that the structural damping is of a viscous nature. In addition, when dampers are incorporated in the design to mitigate the response, their effect is allowed for increasing the building modal damping ratios by a quantity corresponding to the additional energy dissipation arising from the presence of the devices. Even though straightforward, this procedure has some degree of inaccuracy due to the existence of a memory effect, associated with the damping mechanism, which is neglected by a viscous model. In this paper a more realistic viscoelastic model is used to evaluate the response to gust buffeting of tall buildings provided with energy dissipation devices. Both cases of viscous and hysteretic inherent damping are considered, while for the dampers a generic viscoelastic behaviour is assumed. The Laguerre Polynomial Approximation is used to write the equations of motion and find the frequency response functions. The procedure is applied to a 25-story building to quantify the memory effects, and the inaccuracy arising when the latter is neglected.

• Journal of KSNVE
• /
• v.4 no.4
• /
• pp.487-496
• /
• 1994

Recently, the application of viscoelastic material in the field of vibration isolation has gradually increased due to its achievement in structural damping capacity, and many of the theoretical and experimental study has been carried out. In this study, the dynamic characteristics of the visoelastically supported cantilever beam, of which govering equation is based on the Bernoulli- Euler equation, is analyzed theoretically and experimentally. Expression for stiffness of multi-layered viscoelastic materal has been developed using variables such as frequency and number of layers, and further, based on this expression, damping characteristic of the beam is investigated with experimental verification.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 1997.04a
• /
• pp.35-41
• /
• 1997

Viscoelastic materials shows the characteristics of elasticity and viscosity. Unlike metals which show negligible damping value, the damping characteristics of viscoelastic materials like rubber mounts is very important in the analysis of the dynamic system. So there has been a great interest in measuring the damping characteristics of viscoelastic materials. There are two kinds of methods which the damping characteristics can be measured. One is the resonant method where loss factor can be measured only in the resonant frequency. The other is the nonresonant method which is characterized by the impedance method are introduced. The impedance test results, the loss factor by the impedance method are compared to the results of the resonant method and recommendations in the experimental setup are suggested.

• Steel and Composite Structures
• /
• v.48 no.3
• /
• pp.293-303
• /
• 2023

In this paper, geometrically nonlinear free vibration analysis of Mindlin viscoelastic plates with various geometrical and material properties is studied based on the Von-Karman assumptions. A novel solution is proposed in which the nonlinear frequencies of time-dependent plates are predicted according to the nonlinear frequencies of plates not dependent on time. This method greatly reduces the cost of calculations. The viscoelastic properties obey the Boltzmann integral law with constant bulk modulus. The SHPC meshfree method is employed for spatial discretization. The Laplace transformation is used to convert equations from the time domain to the Laplace domain and vice versa. Solving the nonlinear complex eigenvalue problem in the Laplace-Carson domain numerically, the nonlinear frequencies, the nonlinear viscous damping frequencies, and the nonlinear damping ratios are verified and calculated for rectangular, skew, trapezoidal and circular plates with different boundary conditions and different material properties.

• Transactions of the Korean Society for Noise and Vibration Engineering
• /
• v.15 no.12 s.105
• /
• pp.1361-1369
• /
• 2005

Based on a full layerwise displacement shell theory, the nitration and damping characteristics of cylindrical sandwiched panels with viscoelastic layers are investigated. The transverse shear deformation and the normal strain of the cylindrical hybrid panels are fully taken into account for the structural damping modelling. The present finite element model Is formulated by using Hamilton's virtual work principle and the cylindrical curvature of hybrid panels is exactly modeled. Modal loss factors and frequency response functions are analyzed for various structural parameters of cylindrical sandwich panels. Present results show that the full layerwise finite element method can accurately predict the vibration and damping characteristics of the cylindrical hybrid panels with surface damping treatments and constrained layer damping.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2005.11a
• /
• pp.772-778
• /
• 2005

Based on a full layerwise displacement shell theory, the vibration and damping characteristics of cylindrical sandwiched panels with viscoelastic layers are investigated. The transverse shear deformation and the normal strain of the cylindrical hybrid panels are fully taken into account for the structural damping modelling. The present finite element model is formulated by using Hamilton's virtual work principle and the cylindrical curvature of hybrid panels is exactly modeled. Modal loss factors and frequency response functions are analyzed for various structural parameters of cylindrical sandwich panels. Present results show that the full layerwise finite element method can accurately predict the vibration and damping characteristics of the cylindrical hybrid panels with surface damping treatments and constrained layer damping.

• Smart Structures and Systems
• /
• v.30 no.3
• /
• pp.239-243
• /
• 2022

We investigate the influence of nonlinear viscoelastic damping on the response of a cantilever sensor covered by piezoelectric layers in a symmetric or asymmetric configuration. We formulate an initial-boundary-value problem which consistently incorporates both geometric and material nonlinearities including the effect of viscoelastic damping which cannot be ignored for micro- and nano-mechanical sensor operation in a vacuum environment. We employ an asymptotic multiple-scales methodology to yield the system nonlinear frequency response near its primary resonance and employ a model-based estimation procedure to deduce the system damping backone curve from controlled experiments in vacuum. We discuss the effect of nonlinear damping on sensor applications for scanning probe microscopy.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2005.11a
• /
• pp.526-529
• /
• 2005

Attempts have been applied to reduce the vibration of slab. There are several method in the vibration control of slab from a traditional method such as increment of mass or stiffness of slab to a innovative method augmenting damping of slab. In this study, a attempt has been made to increase the effective damping in slab using the viscoelastic dampers made of viscoelastic material. The dampers are installed in a gab between slab and a beam. It is assumed that the stiffness of the beam is infinity for simplicity of the evaluation. we evaluate the reduction effect of the slab selected through numerical simulation and optimization process by applying it to a FEM model. The numerical simulation shows that the effective damping is increased as the number of bean is increased and the vibration control effect is very high.

• International Journal of Precision Engineering and Manufacturing
• /
• v.4 no.1
• /
• pp.37-42
• /
• 2003

Active control of flexural vibrations of smart laminated composite beams has been carried out using piezoceramic sensor/actuator and viscoelastic material. The beams with passive constrained layer damping have been analyzed by formulating the equations of motion through the use of extended Hamilton's principle. The dynamic characteristics such as damping ratio and modal damping of the beam are calculated for various fiber orientations by means of iterative complex eigensolution method. This paper addresses a design strategy of laminated composite under flexural vibrations to design structure with maximum possible damping capacity.

• Steel and Composite Structures
• /
• v.25 no.2
• /
• pp.141-155
• /
• 2017

This paper presents an investigation into the magneto-thermo-mechanical vibration and damping of a viscoelastic functionally graded-carbon nanotubes (FG-CNTs)-reinforced curved microbeam based on Timoshenko beam and strain gradient theories. The structure is surrounded by a viscoelastic medium which is simulated with spring, damper and shear elements. The effective temperature-dependent material properties of the CNTs-reinforced composite beam are obtained using the extended rule of mixture. The structure is assumed to be subjected to a longitudinal magnetic field. The governing equations of motion are derived using Hamilton's principle and solved by employing differential quadrature method (DQM). The effect of various parameter like volume percent and distribution type of CNTs, temperature change, magnetic field, boundary conditions, material length scale parameter, central angle, viscoelastic medium and structural damping on the vibration and damping behaviors of the nanocomposite curved microbeam is examined. The results show that with increasing volume percent of CNTs and considering magnetic field, material length scale parameter and viscoelastic medium, the frequency of the system increases and critically damped situation occurs at higher values of damper constant. In addition, the structure with FGX distribution type of CNTs has the highest stiffness. It is also observed that increasing temperature, structural damping and central angle of curved microbeam decreases the frequency of the system.